While we know that the Earth is warming, do we really know what that means for the future? Is global warming an existential threat to civilization as we know it, or an inconvenient annoyance?
Theoretical physicist Sabine Hossenfelder at the Frankfurth Institute for Advanced Studies has raised that question in a recent New York Times op-ed. The problem is that the problem overwhelms predictability. She also reports on the work of Oxford climate physicist Tim Palmer to support her contention, “What’s less clear is what climate change means for our future.”
The tools science currently has to probe the future consequences of global warming are simply not up to the task, she and Palmer argue. Palmer says, “We know the equations [for predicting the outcomes of climate warming].” Adds Hossenfelder, originally a mathematician, “But we don’t know how to solve them. The many factors that affect the climate interact with one another and give rise to interconnected feedback cycles.”
The 2014 UN Intergovernmental Panel on Climate Change (IPCC) based its often apocalyptic long-term predictions on multiple computer models. “While similar in methodology,” she says, “the models arrive at somewhat different long-term predictions. They all agree that Earth will continue to warm, but disagree on how much and how quickly.”
In a recent paper in Nature Review Physics, Palmer analyzes the problem of prediction of complex interactions: the Navier-Stokes equations, which Wikipedia says “describe the motion of a fluid in space. Solutions to the Navier–Stokes equations are used in many practical applications. However, theoretical understanding of the solutions to these equations is incomplete. In particular, solutions of the Navier–Stokes equations often include turbulence, which remains one of the greatest unsolved problems in physics, despite its immense importance in science and engineering.”
The climate models depend upon Navier-Stokes. The computer simulations divide the globe into pieces on a grid. The computers then calculate how the grid pieces interact. The Navier –Stokes equations, Hossenfelder writes, have “what physicists call ‘scale symmetry,’ meaning it works the same on all distances.”
But Palmer has questioned whether that applies in situations smaller than the grids concocted for the models. Hossenfelder writes, “The Navier-Stokes equation, central to predicting Earth’s climate, is famously difficult to solve and has caused mathematicians and physicists headaches for 200 years.”
What to do? Scale down the grid size in the models? Palmer believes a square kilometer grid, rather than the current 100-km grid, would improve the climate models considerably. But that’s expensive and requires super-scale supercomputers.
That suggests a large international effort and about $1 billion in new funding. So far, no interest, as the European Research Council has backed away from its earlier computing project called Extreme Earth.
Given the stance of the Trump administration toward science in general and global warming in particular, it’s unlikely the U.S. would be funding such a project. Continued ignorance dependent on inadequate models is likely to prevail.
— Kennedy Maize